Translucent sound record



May 1, 1934.

P. A. ROBBINS Y TRANSLUCENT SOUND RECORD Filed March 14, 1931 IIHIII:

311081151 PA.Ro? 2 i"n$ I Patented May 1, 1934 UNITED STATES PATENT ()FFICE 11 Claims.

undulations of sound waves.

' correspondence with the undulations in the bottom of the sound-trace groove in the record.

The invention may be briefly described as follows. In a strip or disk of translucent material, adapted to pass more or less of the rays of ordinary light according to its thickness, is engraved or pressed a sound-trace of the ordinary hill-and-dale type. When such a soundtrace is moved under a source of light, more or less light is transmitted more or less imperfectly reproducing in light the original sound wave undulation.

The perfection of the reproduction is marred, as above suggested, since the undulations of the sound-trace cause, by refraction, concentrations and dispersions of the transmitted light which vary the efiects of the changes in the thickness of the material in which the sound-trace is formed.

To overcome the effects of refraction I fill the sound-trace groove with a material having the same index of refraction as the material of the record. An adhesive such as Canada balsam may be used, if necessary, to cause the adhesion of the filling material. If the material of the record is translucent or semi-transparent, the filling material will be of transparent material. As a variant the record may be of transparent material and the filling of translucent or semitransparent material, since the thickness or the filling varies with the depth of the sound-trace.

The invention also includes certain details of construction as hereinafter specifically described and as illustrated in the accompanying drawing in which Fig. 1 is an enlarged diagrammatic section of part of a record taken lengthwise of the soundtrace and with the filling omitted;

Fig. 2 a similar view with the filling applied; Fig. 3 a similar view of part of a disk record; Fig. 4 a cross section on the same scale of part of a disk record;

Fig. 5 a perspective detail of the slitted end of the lens carrier;

Fig. 6 a plan view, on a small scale of the disk record shown in Fig. 4.

In the drawing like numerals of reference indicate corresponding parts in the different figures.

Referring to Figs. 1 and 2 of the drawing, 1 is part of a film strip formed of a semi-transparent material such as tinted celluloid. In this film strip has been formed a sound-trace 2 of the known hill-and-dale type. This sound-trace may be engraved in the film material by apparatus such as shown and described in my co-pending application 445,781, filed April 19, 1930. The thickness of the strip between the bottom of the sound-trace and the lower surface of the film strip, and therefore the degree of opacity, varies, passing more or less light in proportion to the thickness of the film. This effect is varied due to the irregular refraction of light rays passing through the film in consecutive positions, as indicated by the dotted lines 3 in Fig. 1. The light rays are refracted in an irregular manner from side to side of a necessary constant path, and it is therefore impossible to direct them constantly onto a light-sensitive cell and thus cause variations in the fiow of current through the cell in correspondence with the variations in thickness of tinted celluloid through which the light passes.

I aim to produce gradual fluctuations in current strength through the light-sensitive cell in exact correspondence with the undulations in the bottom of the sound-trace groove, and to accomplish this it is necessary to overcome the refraction of the light beam when passing into the film, so that at all positions the light rays will be parallel and thus the intensity and amount of light will vary in accordance with the thickness of material it has travelled through in the partly opaque film at the bottom of the sound trace- In Fig. 2 is shown how this is accomplished. The a sound-trace has been filled with a material 4 having substantially the same index of refraction as the material of the film strip itself. The filling material is transparent to light rays, the variations in the intensity of the light passing through the sound-trace being therefore due solely to the variations in the thickness of the material of the film strip at the bottom of the sound trace. The reverse arrangement is also possible, that is the film strip may be of transparent material and the filling of semi-transparent or tinted material. The filling material may be applied to the sound-trace groove as a liquid and allowed to harden, or it may be a thermo-plastic solid softened by heat and pressed or rolled into the sound-trace groove. A thin cement of suitable adhesive, such as Canada balsam, may be applied between the filling material and the groove surfaces.

In Figs. 3 and 4 I show my invention as applied to a disc record l in which the soundtrace is formed by any known means from a master record. The disc will usually be formed of semi-transparent material and the sound trace recorded in its surface in the form of a spiral groove with an undulatory bottom.

The next step is to render the sound groove non-refractive to abeam of light directed through the sound-trace in a direction approximately normal to the surface of the record disc. On top of the record disk is placed a transparent disk 4 of thermo-plastic transparent material having the same index of refraction as the material of the disc 1 A thin film of Canada balsam may be used to secure adhesion between the discs. Preferably the disc 4 is applied to the disc 1 in vacuo, so as to prevent the inclusion of any air between the two discs which would cause refractions interfering with the passage of the light of the refraction where the two discs are in contact.

Intermediate the position of the convolutions of the sound-trace, grooves 6 may be formed in the disc 1 for engagement with a guide, not shown, of the reproducing apparatus. The soundtrace groove in an ordinary phonograph record is about one-ninetieth of an inch wide. The undulations in the bottom of the sound-trace are measured in thousandths of an inch. Along the length of the sound-trace the undulations occur at intervals of minute fractions of an inch. Owing to the smallness of these dimensions it is difficult to form a light beam which is free from aberration, for light passing through a small orifice is subject to diffraction. This diificulty is partly overcome by the novel constructions shown in Fig. 4, which is a section transversely of the grooves of a disc record.

Between the convolutions of the guide groove 6 and in alinement with the bottom of the soundtrace 2 the under surface of the record disc is formed with a spiral concave groove 7, which acts as a diverging refractor for light rays emerging from the record. The upper surface of the disc 4 is formed with a spiral convex ridge 8, which acts as a converging refractor for light rays passing into the record disk. 9 is a lens for directing a beam of light onto a record. The beam is refracted by the ridge 8 to concentrate the rays in the bottom of the sound-trace groove. Any ray which falls to one side of the soundtrace groove will be refracted into an adjacent convolution of the sound-trace groove by the adjacent convolution of theridge 8. This prevents scattered rays from interfering with useful rays. Upon emerging from the bottom of the record the useful rays of light are divaricated by the concave groove and directed through the narrow slit 11 to the lens 12 and thence to a mirror 13' from which they are directed to a light sensitive cell, not shown. The slit 11 has its long dimension at right angles to the course of the sound trace groove. By this means the useful rays of light are focused on the desired point without interference from vagrant rays scattered from their intended course by refraction and reflection due to imperfections in the apparatus.

What I claim as my invention is:

1. A sound record formed of a tinted material semi-transparent to light rays, the sound trace being formed by variations in the thickness of successive portions of its length corresponding to the undulations of sound waves and thus adapted to pass more or less light in correspondence with such sound waves.

2. A sound record comprising two sheets of material having substantially the same index of refraction, one being transparent and the other semi-transparent to light rays and secured together in intimate contact, the contacting surfaces having complementary sound-traces formed therein of the hill-and-dale type, whereby successive portions of the record are adapted to pass more or less light in accordance with said soundtrace.

3. A sound record formed of a material semitransparent to light rays, the sound trace being formed by variations in the thickness of successive portions of its length corresponding to the undulations of sound waves and thus adapted to pass more or less light in correspondence with such sound waves, the record being provided with a groove in one of its two opposite faces paralleling the length of the sound trace.

4. A sound record formed of a material semitransparent to light rays, the sound trace being formed by variations in the thickness of successive portions of its length corresponding to the undulations of sound waves and thus adapted to pass more or less light in correspondence with such sound waves, the record being provided with a concave groove in one of its two opposite faces alined with the sound trace.

5. A sound record formed of a material semitransparent to light rays, the sound trace being formed by variations in the thickness of successive portions of its length corresponding to the undulations of sound waves and thus adapted to pass more or less light in corespondence with such sound waves, the record being provided with a convex rib at one face alined with the sound trace and at the other face directly opposite with a concave groove.

6. A sound record formed of a material semi.- transparent to light rays, the sound trace being formed by variations in the thickness of successive portions of its length corresponding to the undulations of sound waves and thus adapted to pass more or less light in correspondence with such sound waves, the record being provided at one of its two opposite faces with a convex rib alined with the sound trace and at the other face directly opposite with a concave groove and in one of said faces with a groove paralleling the length of the sound trace.

7. A sound record of the disk type provided with a spiral sound trace formed by variations in i.

the thickness of successive portions of its length corresponding to the undulations of sound waves and thus adapted to pass more or less light in correspondence with such sound waves and with a spiral grove in one of its two opposite faces paralleling the length of the sound trace.

8. A sound record of the disk type provided with a spiral sound trace formed by variations in the thickness of successive portions of its length corresponding to the undulations of sound waves and thus adapted to pass more or less light in correspondence with such sound waves and with a spiral concave groove in one face in alinement with the sound trace.

9. A sound record of the disk type provided with a spiralsound trace formed by variations length corresponding to the undulations of sound waves, and thus adapted to pass more or less light in correspondence with such sound waves and with a spiral convex rib in one face in alinement with the length of said sound trace and at the other face, directly opposite, with a concave grove.

10. A sound record formed or tinted material semi-transparent to light rays, the sound trace being a groove which has a bottom undulatory along its length in correspondence with the undulations of sound waves, and variations in thickness of said tinted material in correspondence with said undulations in said groove bottom, the soundtrace groove being filled with a relatively transparent material having substantially the same index of refraction as the material in which the sound-trace groove is formed; a convex ridge on one surface of the record; and a concave groove on the opposite record surface the said convex ridge and the said concave groove and the said sound-trace groove being alined with one another throughout their lengths and positioned relatively so that the median lines of the convex ridge the concave groove and the sound-trace groove all lie in the one plane substantially normal to the plane of the record surfaces.

11. A sound record formed in accordance with claim 10 having a groove formed in one of its surfaces parallel to but not alined with the convex ridge and the concave groove.

PERCY A. ROBBINS. 

